As the first independent application led by a recipient of NCI K07 Award (Molecular Epidemiology of Colorectal Cancer), this proposal addresses hypotheses in epigenetics and epidemiology of colorectal cancer, in response to NIH Program Announcement PA- 09-234 (Diet, Epigenetic Events, and Cancer Prevention). Colorectal cancer is the second leading cause of cancer death in the United States. Abnormal DNA methylation patterns are a hallmark of most cancers including colorectal cancer. Furthermore, DNA methylation alterations (such as loss of imprinting) in non-cancerous cells may predispose to cancer development. Importantly, epigenetic changes, including DNA methylation alterations, are reversible and thus can be targets for therapy or chemoprevention. Accumulating evidence suggests that dietary factors (e.g., alcohol and one-carbon nutrients such as B vitamins) may affect cellular epigenetic status. Examining how dietary factors influence epigenetic alterations is important for better understanding of colorectal cancer development and progression, which can provide a scientific basis for dietary recommendations and help optimize preventive strategies. For that purpose, we will utilize the resources of two large prospective cohort studies, the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). Both cohort studies provide dietary data over a 20-year period, DNA from blood cells, long-term survival data, and paraffin-embedded tissue of colorectal cancers. We anticipate over 4500 incident colorectal cancer cases up to 2012 in these cohorts, and among those, paraffin-embedded tissue materials will be available in over 3000 cases. We propose to examine the interrelationship between intake of dietary one-carbon nutrients and alcohol, colorectal cancer risk, cellular epigenetic changes, and clinical outcome. In addition, we will utilize data resulting from genome-wide expression profiling of 1000 colorectal cancers in the cohorts (which has been ongoing with separate funding supports) to discover genes potentially related to abnormal one-carbon metabolism as well as specific epigenomic aberrations in colorectal cancer. Thus, we are in a unique position to examine the relations between modifiable dietary factors, epigenetic and epigenomic aberrations, and genome-wide expression patterns in tumor cells. Through better understanding of epigenetic mechanisms of carcinogenesis, we can propose preventive measures for the incidence and mortality from colorectal cancer.